Gypsum wallboard and method for producing same



June 18, 1968 0. BIERI ET AL GYPSUM WALLBOARD AND METHOD FOR PRODUCINGSAME Filed Jan. 21, 1966 INVENTOR. David Bieri y Edward S. Coin ATTORNEYUnited States Patent 3,339,042 GYPSUM WALLBOARD AND METHOD F PRODUCINGSAME David Bieri, Tonawanda, and Edward S. Coia, Kenmore, N.Y.,assignors to National Gypsum Company, Buffalo, N.Y., a corporation ofDelaware v Continuation-impart of application Ser. No. 344,582, Feb. 13,1964. This application Jan. 21, 1966, Ser. No. 522,094 a 18 Claims. (Cl.161-41) ABSTRACT OF THE DISCLOSURE A paper-covered, gypsum corewallboard made of cover paper having therein, or thereon, a curedhydrophobic organo-silicone, which reduces the absorption by the paperof components of the wet gypsum slurry, without affecting substantiallythe paper porosity, and, of prime importance, without any deleteriouseffect on the bond of the paper to the gypsum core, either prior to thedrying of the board or after the drying of the board.

This application is a continuation-in-part of our copending applicationentitled Gypsum Wallboard bearing Ser. No. 344,582 and filed Feb. 13,1964, now abandoned.

This invention relates to an improved gypsum board, and to the new andunobvious method of making the improved gypsum board.

Gypsum wallboard is manufactured, for example, in what might be thoughtof as two steps or operations. First, there is manufactured a papercover sheet, generally a multiply sheet manufactured on a cylindermachine in which a cylindrical screen rotates in a vat containing anaqueous slurry of paper furnish. Conventional sizing compounds such asrosin and alum are added to the selected vat to properly size some orall plies. Various numbers of plies after being formed on the screen,are removed therefrom and are superimposed to form an essentiallyunitary piece of paper, typically of about 0.020 inch thick.

In the gypsum board plant, as a second step, an aqueous slurry ofsettable gypsum plaster, having more than sufiicient water for hydrationand setting of the gypsum, is spread on the advancing paper cover sheetand a second paper cover sheet is continuously applied on top of thegypsum as the unset, wet board is moved through the forming apparatus.The partially hardened, endless board is then cut into desired lengthsand passed into a high temperature drying kiln. l

The paper ply of the multi-ply cover sheet directly adjacent the plastercore is known as the bond ply or core-side ply. This ply, and the fillerplies intermediate the bond ply and the outermost ply or top liner ply,are commonly formed from a mixture of waste paper pulps. The bond ply,top liner ply and filler plies may be made of substantially the same ordifferent paper furnish. For example, the bond ply and filler pliesformed from a mixture of waste paper pulps can be employed in themanufacture of the paper cover sheet. Where an attractive outermost plyis required, such as creamface, it may be made from groundwood andsulfite or other type of suitable pulp.

Generally, the paper cover sheets used in gypsum wallboard range inthickness from about 0.010 to 0.030 inch, and preferably 0.016 to 0.023inch, and have tensile strengths in the machine direction of about50-115 'ice lbs/in. and in the across-machine direction within the rangeof about 15401bs./in. ,1 s n It is necessary to have a strong bondbetween the gypsum core and the paper cover sheet in the finished boardto prevent separation or delaminationof the paper from the core.Separation can occur either in the form of film peeling" in which a thinlayer of the core is removed along with the paper and adheres thereto,or a clean peel in which the paperis cleanly separated from the gypsumcore. a r

Generally, it has been considered necessaryto provide for absorption ofwater from the gypsum; slurry into at least the bond ply of themulti-ply paper covering sheet. The water absorption mechanism carriessome dissolved gypsum into the paper where the gypsum crystallizes andprovides a resultant mechanical linkingof the paper to the gypsum core.This absorption of water by the paper, however, decreases the ratio ofwater to. unset gypsum in a very thin layer of the gypsum coreimmediately adjacent the paper cover sheet, particularly during initialsetting of the gypsum core, when the ratio of water to gypsum iscritical to obtain the desired quality of set gypsum throughout thecore. In the thin layer of unset gypsum having a relatively lower waterratio, a different crystal growth occurs from that throughout thebalance of the core, creating what is. termed stratification.Stratification becomes increasingly apparent with efforts to acceleratethe setting of the gypsum, or to decrease the drying time in the kiln.Also, gypsum manufactured from ores of relatively low purity mayaggravate the problem.

As the degree of stratification increases, the tendency of the thinlayer of gypsum to become recalcined during drying in the kilnincreases. Accordingly, stratification creates a limiting factor in thedrying speed and thus in the overall production rate for a manufacturingfacil ity. It the two stratified layers of gypsum adjacent the two papercover sheets become recalcined during drying, the integrity and strengthof the core at these layers is reduced permitting the cover sheets to besusceptible to so-called film peeling which is manifested by separationof the paper from the core with a thin layer of the core adhering to thepaper. I

The tendency toward recalcination of the stratified layers of gypsum canbe lessened, for example, by adding a small percentage of starch, orother suitable waterretention agent, to the gypsum mix used to form thecore, The starch migrates toward, and partially into, the paper duringthe drying and, by its hydrophilie nature, tends to retain waterwherever the starch becomes concentrated, including generally theinterface zone where the stratification occurs. The greater portion ofthe starch, however, migrates into the paper because of theabsorptiveness of the paper. Where a loss of starch from the gypsum coreto the paper occurs, another type of papercore separation, known asclean peel, occurs wherein the paper cleanly separates from the cOrewith substantially no core particles clinging to it. For suflicientprotection against recalcination in the zone of stratification and tocompensate for starch loss, a larger amount of starch is generallynecessary than would be necessary if the starch could be concentrated inthe outermost zone of the gypsum core.

The additional amounts of starch required in a core formulation, asabove stated, and the absorptivity of the paper cover sheet necessitategreater portions of water in forming the core, thus increasing theamount of drying ultimately required and deleteriously affecting therate at which the board can be manufactured with given dryingfacilities.

In addition to the problems of separation or delamination at theinterface between the gypsum core and the cover sheets, the multi-plypaper cover sheets are also subject to intra-ply separation and/ordelamination of each of the plies from the other during the board-dryingoperation. Various techniques have been utilized to obviate delaminationof the plies, such as the inclusion of wet strength resins in the papercover sheet. Aminoplastic resins such as melamine-formaldehyde orurea-formaldehyde resins are commonly employed, and the resins arepreferably added during the paper-making stage of the gypsum boardmanufacturing operation. While the use of aminoplastic resins forimparting wet strength to the paper plies minimizes delamination of thepaper plies, this is an added expense in the cost of manufacture.

In further investigations of the problems of stratification,recalcination and delamination, the face of the paper cover sheet incontact with the gypsum core was treated with a suitable material whichwould make it highly repellant to water, or more specificallynon-absorptive, without substantially decreasing the normal porosity ofthe paper. Suitable materials which effect this objective and treatingtechniques are described in copending United States application Ser. No.833,281, filed Aug. 12, 1959, by David Bieri, now Patent No. 3,307,987.

In accordance with our invention, it now has been found that the bondbetween the paper cover sheet and the gypsum core is unexpectedlystrengthened and the problems of stratification, recalcination anddelamination minimized are avoided by treating the paper cover sheetwith a curable hydrophobic organosilicone. As an additional advantage,gypsum board made in accordance with our invention requires less starchthan normally employed, and reduces the amount of conventional sizingsuch as with rosin and alum, that is normally required. In addition, theinvention facilitates drying of the gypsum board and provides a gypsumboard having an excellent bond between the paper cover sheet and thegypsum core such that substantially all board has what is referred to inthe trade as 100% bond; that is, the paper to the core bond is at leastas strong as the cohesive strength of either the core or the paper bythemselves. Still further, this invention minimizes or inhibitsdelamination of the paper plies during the board-drying operationthereby obviating or lessening the need of the aminoplastic wet strengthresins in the paper cover sheet. Where desired, however, a suitable wetstrength resin may be incorporated with the paper cover sheet which isalso treated with a curable hydrophobic silicone, but the amount of wetstrength resin used is reduced substantially from that required in theabsence of the treatment according to this invention.

According to the present invention, the paper cover sheet is treatedwith a curable hydrophobic organo-silicone, and more preferably acurable hydrophobic silicone selected from the group consisting oforganohydrogensiloxane, epoxy silicone, and the addition product of ahydrosilicone with a fatty acid ester. The silicone compositions aremore fully described infra.

The amount of curable hydrophobic silicone required to minimize orinhibit stratification will vary with variations in paper and gypsumcomposition. The inhibition of stratification to be achieved when apaper is used that has been given the silicone treatment of thisinvention can generally be predetermined to some extent by measuring thereduction in water absorption of the silicone-treated paper asdetermined by the Cobb test, described below. As water absorption by thesilicone-treated paper is decreased, inhibition of stratificationusually increases. Furthermore, as the amount of silicone used in thetreatment increases, water absorption decreases and as a resultinhibition of stratification increases.

The Cobb test follows the general test outlined by T.A.P.P.I., but ismodified as follows: In conducting this test, a 5" x 5 sample of thepaper to be tested is conditioned at 150 F. for minutes and cooled in adesiccator. Upon removal from the desiccator, it is weighed rapidly on abalance to the nearest 0.01 gm. This is the dry weight. The sample isthen clamped in a standard sq. cm. Cobb ring (manufactured by W. and L.E. Gurley Instrument Co.) having an area of 100 square centimeters withthe paper surface to be tested exposed. The Cobb ring is pre-heated to100-420 F. prior to conducting the test in order to prevent rapidcooling of the test water. 150 ml. of clean tap water at F. is thenpoured into the Cobb ring, covering the surface of the paper sample tobe tested. A timer is started as soon as the water is poured into thering. After the 'water has been in contact with the paper for exactly 3minutes, the water is poured out of the ring. As rapidly as possibile,the paper sample in removed from the ring, blotted dry of surface waterwith a highly absorbent blotter or paper towel, folded into quarters toreduce weigh-t loss from evaporation, and reweighed to the nearest 0.01gm. This is the wet weight. (This last sequence of steps should notexceed 1530 seconds). The Cob-b value is determined by subtracting thedry weight from the wet weight.

It is desirable to have a Cobb value for the siliconetreated paper coversheet at the time the gypsum board is manufactured of about 0.4 to about1.0 gram, and more preferably about 0.4 to 0.7 gram, as measured on thesurface of the paper cover sheet adjacent the gypsum core.

It is desirable that the side of the paper cover sheet adjacent thegypsum core contain cured hydrophobic silicone, and for that reason itis expedient to treat the coreside of the paper cover sheet, asdescribed in greater detail herein-below. It should be understood,however, that the paper cover sheet may contain the hydrophobic siliconethrough a substantial depth thereof and that several or all plies of thesheet may contain the silicone. The paper cover sheet can contain thecured hydrophobic silicone in the space from the surface of the papersheet adjacent the gypsum core to a location displaced inwardly of thepaper from said surface, which may include up to the thickness of thesheet. For example, in the manufacture of multiply paper cover sheet ona cylinder paper-making machine, the bond ply adjacent the gypsum coremay be treated in accordance with this invention either alone or incombination with one or more of the filler plies and/or the top liner.When the silicone is applied to the bond ply of the paper cover sheet asby means of a roller applicator at the calender stack, described belowin greater detail, the bond ply and adjacent filler ply or plies,generally about 2 to 4 of the adjacent filler plies, are found tocontain silicone.

The hydrophobic organo-silicone may be impregnated or incorporated intothe paper cover sheet in numerous ways, i.e., spraying, brushing,flooding, rolling or adding the silicone to the furnish for the paper.After the paper cover sheet is treated, the hydrophobic silicone iscured to effect cross linking. The rate of cure will differ for eachspecific hydrophobic silicone, and the curing rate is affected by suchfactors as temperature, time and total acidity of the paper-makingsystem. For this reason, it usually is expedient to treat the papercover sheet with the hydrophobic silicone during the course ofmanufacture of the paper, whereby the elevated temperatures employed inthe calendaring stage will efiect, to some degree, curing of thesilicone. Regardless of the rate of cure, it is important that thehydrophobic silicone incorporated in the paper cover sheet besubstantially cured prior to the manufacture of the gypsum board.

Where desired, the rate of cure of the hydrophobic silicone incorporatedin the paper may be accelerated by the use of suitable catalysts. Anumber of catalysts are known and available which will effect the crosslinking of the hydrophobic silicone treating agent. Suitable catalystsinclude the metal salts of organic acids, for example, lead, iron, zinc,copper, aluminum, magnesium, cadmium, cobalt, nickel, tin and sodiumsalts of acetic,

octoic, oleic, stearic, naphthenic, lauric and resin acids,

or mixtures thereof. These metal salts might include a dialkyl methyldiester of an organic acid, such as dibutyl tin dilaurate, dibutyl tindiacetate, dibutyl tin di- 2-ethyl hexoate, and the like.

The hydrophobic silicone can be employed in the treatment of the papercover sheet in undiluted form, but it is preferable to use a solution oraqueous emulsion in order to more readily control the amount applied.Aqueous emulsions of the hydrophobic silicone are preferred, and can beprepared in conventional manner with conventional emulsifying agents.Quaternary ammonium salts, the higher aliphatic alcohol sulfates, orpolyoxyethylene derivative of polyhydric alcohols are typicalemulsifying agents which can be used. These include, for example,cationic agents such as N-cetyl-ethyl morpholinium etho sulfate, orn-alkyl trimethyl ammonium chlorides; anionic agents such as laurylalcohol sulfate; and nonionic agents such as nonyl phenyl polyethyleneglycol ether, polyoxyethylene sorbitan monolaurate, and polyoxyethylenecetyl ether. Certain of these emulsions may be unstable, such as themethyl hydrogen silicone emulsion which tends to eliminate hydrogen onstanding. This condition may be avoided by adding an organic acid, suchas acetic acid, to the emulsion in order to inhibit the evolution ofsilane hydrogen.

The hydrophobic silicone, preferably as an aqueous emulsion, is appliedto or incorporated in the paper cover sheet for gypsum board in any oneof a number of ways. Where desired, the hydrophobic silicone may beapplied to the paper in conjunction with a suitable curing resin. Themethods of application include, for example, the following:

(1) Separate spray, flooding or roller application of the hydrophobicsilicone to the paper web at the dryer section of the paper-makingprocess.

(2) Separate spray, flooding or roller application of the hydrophobicsilicone to the paper web as it is formed at the cylinders or on afourdrinier wire of the paper machine.

(3) Continuous addition of the hydrophobic silicone to the paper furnishat one or more plies prior to forming on the paper-making machine.

It is to be understood that these methods of application areillustrative, and other techniques will be apparent to those skilled inthe art to which this invention pertains. A suitable curing catalyst maybe applied to the paper by the same or dilferent technique from thatused in applying the hydrophobic silicone; and the catalyst may beapplied shortly before, simultaneous with, or after the addition of thehydrophobic silicone to the paper. For example, the hydrophobic siliconemay be applied to the paper by roller application at the dryer sectionof the papermaking process, and thereafter the catalyst may be appliedby spraying with a suitable nozzle. As a further illustration, thecatalyst may be added continuously to the paper furnish for one or moreof the plies prior to forming on the paper-making machine, andthereafter applying the hydrophobic silicone to the paper stock prior tothe formation or after formation of the paper web.

The amount of cured hydrophoric slicone incorpo rated in the paper isand should be suflicient to effect the objectives of this invention.This amount will depend primarily upon operating conditions such asmachine speeds, composition of the paper, nip pressure or doctor bladeadjustment where flooding or roller applications are used, sprayconditions where employed, as well as temperature, viscosity andcomposition of the silicone compound. Generally, about 0.1 to 4 poundsof cured hydrophobic silicone solids per ton of paper treated on oneside will give satisfactory results, and more preferably about 0.2 to 2pounds, for a conventional wallboard multi-ply cover sheet typicallyhaving a thickness of about 0.020 inch. Where an amount less than 0.1pound is used, the desired qualities are to some extent reduced. On theother hand, generally there is no additional benefit in employing morethan 4 pounds of silicone solids.

When a catalyst is used for curing the hydrophobic silicone, the amountemployed will depend in part upon the time required to promote curebefore the paper is used in making gypsum board. The rate of curenormally can be accelerated by increasing the amount of catalyst, suchthat where the time lapse between the paper manufacture and gypsum boardmanufacture is at a minimum, greater amounts of catalyst can be usedthan where there is a substantially longer time lapse. About 0.1 toabout 3 pounds of catalyst solids per tone of treated paper will giveeffective results, but greater or lesser amounts can be used.

Curing times sufiicient to provide the desired cure or cross linking ofthe hydrophobic silicone are used. For example, there was applied to thepaper cover sheet at the surface of the bond ply or core-side ply 0.5pound of a methyl hydrogen polysiloxane having the general structuralformula:

w I i CH -Si-O SIiO]Si-CH CH3 CH; H3 1 wherein n has an average value offrom 30 to 35. Dibutyltin diacetate, as catalyst, and the silicone wereapplied to the paper at the calendering operation where the temperatureranged from a high of about 225 F. to a low of F., and curing of thecompound was substantially effected in the paper stored at roomtemperature after 12 hours. Under the same operating conditions butwithout catalyst, 0.5 pound of epoxy silicone applied to the paper wascured after 10 days. When the catalyst was employed with the epoxysilicone, curing was complete after about 2 to 3 hours.

As explained above, the rate of cure may be increased by adjustingcertain factors in the paper-making procedure, such as increasing thetemperature at which the cure is being carried out, adjusting the totalacidity of the paper-making system or by the use of a catalyst. Theextent of cure can be evaluated by the Cobb value of the paper after agiven elapsed time. The cured silicone present in the paper reduceswater absorption by the paper, as determined by the Cobb test, and themore silicone cured at the time the board is manufactured, the more thewater absorption is decreased thereby increasing inhibition ofstratification.

There is illustrated schematically in the drawing a technique forapplying the hydrophobic silicone to the paper cover sheet. There isshown the calender section of a conventional multi-cylinder paper-makingmachine. Prior to being dried, the multi-ply sheet =10 is assembled intoa laminated sheet by forming a plurality of plies which are subsequentlylaminated after being passed through the press part of the machine (notshown). The finished paper cover sheet 10, which is generally seven,eight or nine ply, consists of a bottom liner ply or 'bond ply which isin contact with the gypsum core, a top liner ply which is the exposedply and sever-a1 'filler plies. Thereafter, sheet 10 is passed through ahigh temperature dryer (not shown), and then over a wet 'palender stackof rolls 11 and further calendered by passing the sheet 10 over a drycalender stack of rolls 112 typically at a speed of about 300 to 5'00feet per minute dependingprimarily upon the weight of paper beingmanufactured. After leaving the calender section, sheet 10 is furtherprocessed into the final cover sheet which is then used either applyingthe curing catalyst at the bottom roll of the wet calender stack, oratlernatively, applying the hydrophobic silicone at the bottom roll ofthe wet calender stack and the curing catalyst at the bottom roll of thedry calender stack. Where desired, the catalyst may be omitted, and inthat case it is desirable to apply the hydrophobic silicone at trough13.

The applicator troughs 13 and 14 are used to flood the paper with therequired amount of hydrophobic silicone and catalyst. A suitable feedingtechnique (not shown) is utilized to insure that the applicator troughs13 and 14 remain full during the application of the hydrophobic siliconeand catalyst to the surface of the bond ply of the paper {cover sheet.By this means, the hydrophobic silicone, and catalyst when used, areapplied substantially uniformly to the surface of the paper. The paperis impregnated with the silicone composition, and in a typicaloperation, approximately half of the silicone is present in the bondply, and over half of the silicone is present in the bond ply and thefiller ply immediately adjacent thereto. Minor amounts of silicone arepresent in the next one or two adjacent filler plies. For example, in anoperation such as described in Example 1 below, about 50% silicone wasfound in the bond ply, about 26% in the ply adjacent thereto, about 12%in the next adjacent ply and lesser amounts in the next two adjacentplies. This, of course will vary depending on dilution of the silicone,the extent of rosin sizing, and other factors.

The treated paper and gypsum slurry are integrated at the board plant,and the formed board, cut to desired lengths, is passed through a dryingkiln. In the manufacture of a inch board, for example, using papertreated with n epoxy silicone or with the silicone of Formula 1, theboard passes first through a high temperature zone of about 400-550 F.,then through an intermediate zone of about 350450 F., and then through adry end zone of about ZOO-300 R, which typically takes about 50 to 70minutes.

In addition to minimizing stratification, other attendant advantages ofthe instant invention include the production of high quality gypsumboard employing substantially lesser amounts of starch in the gypsumcore than normally utilized. It was found that by reason of ourinvention as much as 40-80% savings in the amount of starch was realizedwithout impairing overall board quality. For example, one productionfacility which previously required about 12 pounds of starch perthousand square feet of paper cover sheet for /2 inch wallboard was ableto reduce starch usage to about 5 pounds per thousand square feet forthe same wallboard, when using paper treated in accordance with thisinvention. Another facility with somewhat different board producingequipment and operating conditions previously required 9 pounds ofstarch per thousand square feet of paper cover sheet for /2 inlchwallboard, and in using paper treated by this invention has run as lowas 2 pounds of starch per thousand square feet for the same sizewallboard. As is known in the art, the amount of starch used in thegypsum core depends on a number of factors including, for example,gypsum rock purity, manufacturing speeds, versatility of dryingfacilities, etc., and this generally is true with respect to wallboardmanufactured according to conventional procedures as well as thatmanufactured according to our invention.

As a still further advantage of this invention, the conventional sizewith rosin and alum may be generally omitted from one or more plies. Forexample, when the core side surface of the paper cover sheet is treatedas by roller application with a silicone compound in accordance withthis invention, the rosin-alum sizing can be omitted from the bond plyand one or more of the tiller plies, preferably the filler plyimmediately adjacent the bond ply. In such a case, it is desirable thatno rosinalum sizing be used in the paper cover sheet to a thickness ofabout 0.008-0011 inch of the paper as measured from the outer surface ofthe bond ply to the filler plies. The reason for this is that papersexhibiting low bottom Cobb, e.g., paper being relatively nonabsorptive,can result in loss of wet bond of the paper to the core at the knifewhen cutting the wet endless board into required lengths. Wet bond isthe phenomina where when the paper is pulled from the core of the boardprior to drying, the paper has become sufficiently wet such that thefiber bond is weakened sufiiciently to permit the paper to tear apartthus leaving some paper adhered to the Wet core. In making a gypsumwallboard in accordance with the invention, the rosin-alum sizing isomitted from the bond ply and can also be omitted from one or more ofthe filler plies as described in order to attain the desired Wet bondingat the board plant knife. As a result, considerable savings inrosin-alum sizing are realized.

The silicone-containing compounds suitable for treating the paper coversheet for gypsum wallboard in accordance with the process of ourinvention are those compounds which can be termed curable hydrophobicsilicones, and include both monomeric and polymeric species, i.e., thesilanes and siloxanes having these two properties. Suitable monomericsilicone compounds as being typical for use in the invention are thesilane esters such as acyloxysilanes, the alkoxy silanes, the waterhydrolyzable silanes such as methyl sodium silanolates, and the wellknown alkylcl'llorosilanes such as dimethyldichlorosilane.

Illustrative of the acyloxysilanes are octadecoxy-dodecoxy-propoxysilicone acetate, di-octadecoxy-propoxysilicone acetate, tridodeeoxysilicone formate, etc. Methods for preparation of these esters can befound in United States Patent 2,405,988.

Alkoxy silanes found suitable include, for example, ethoxysilane,diethoxysilane, dimethoxydichlorosilane and diethoxydifluorosilane.Suitable alkylchlorosilanes include, for example,dimethyldichlorosilane, ethyltrichlorosilane, and the like.

Suitable curable hydrophobic silicone compounds include also theisocyanato modified silanes and siloxanes. Examples includeisocyanatophenyl(methyl)dichlorosilane, isocyanatophenyltrichlorosilane,isocyanatophenyldimethylchlorosilane, betaisocyanatophenylethyldiethoxyfiuorosilane,delta-isocyanatobutyl(methyl)difluorosilane,gamma-isocyanatopropyl(butoxy)dichlorosilane, andisocyanatocyclohexyldifiuorosilane, and siloxanes shown in the followingformulae:

I L a .izno

2 wherein R is a monovalent hydrocarbon radical, a is a number having avalue from to 1 inclusive, b is a numher having a value from 1 to 2inclusive, and the sum of [1+]; has a value of from 1.5 to about 2. Suchorganohydrogensiloxanes can be hydrocarbylhydrogen-siloxanes orcopolymers of hydrocarbyl siloxanes with dihydrogensiloxanes. Themonovalent hydrocarbon radicals represented by R in the above Formula 2are illustrated by alkyl groups, such as methyl, ethyl, propyl,isopropyl, butyl, isobutyl, amyl, hexyl and the like; aryl groups, suchas phenyl, naphthyl and the like; alkaryl groups, such as tolyl,ethylphenyl, xylyl, mesityl and the like; aralkyl groups, such asbenzyl, phenylethyl and the like; alkenyl groups, such as vinyl, allyl,and the like; and alicyclic groups, such as cyclopentyl, cyclohexyl andthe like. More desirably, R is an alkyl group, and in the preferredembodiment R is a methyl group. The organohydrogensiloxanes of the aboveFormula 2 can be cyclic polymers consisting generally of from 3 to 7organohydrogensiloxane units or they can be substantially linearpolymers endblocked with triorganosilyl units, hydroxyl groups or alkoxygroups, for example. Such substantially linear polymers generally havechain lengths such as to provide viscosity values of from about 10 toabout 1,000,000, preferably from about to 200, centistokes at C.Preferably, the organohydrogensiloxane is a rnethylhydrogensiloxanehaving a viscosity value of from about 15 to about 50 centistokes at 25C.

The organohydrogensiloxanes of greatest utility should contain fromabout 0.04 to about 1.7 weight percent silanic hydrogen. Theorganohydrogensiloxanes having the above Formula 2 and containingsilanic hydrogen can also be combined as a copolymer or blend, forexample, with organosiloxanes of the unit formula:

2 (3) wherein R is defined above for Formula 2 and c is a number from 1to 3, inclusive. The organosiloxanes of the above Formula 3 can becyclic polymers consisting gen erally of from 3 to about 7 siloxaneunits or they can be substantially linear polymers end-blocked withtriorganosilyl units, hydroxyl groups or alkoxy groups, for example.They can be end-blockers for siloxanes of Formula 2 or they can betrifunctional resin-like materials. These organosiloxanes resulting froma copolymer or blend of materials having Formulas 2 and 3 should containfrom about 0.04 to about 1.7 weight percent silanic hydrogen. The epoxysilicones, also of a polymeric type, found suitable for this inventionhave, for example, a general unit formula:

wherein D represents an R SiO unit in which R is a monovalenthydrocarbon radical free of acetylenic unsaturation;

of acetylenic unsaturation; R is a monovalent organic radical containingat least one vicinal epoxy group; and M and M are in each occurrence thesame or different end-blocking unit having the formula:

IVE-Sl ws in which R" is a monovalent hydrocarbon radical free ofolefinic unsaturation, preferably an alkyl group containing from 1 to 6carbon atoms or a hydrocarbyloxy radical in which the hydrocarbyl moietyis free of olefinic unsaturation and is preferably an alkoxy groupcontaining from 1 to 10 carbon atoms or M and M can be: alkoxy radicals.R is a monovalent organic radical containing a vicinal epoxy group; ahas a value from 0 to 1 inclusive; q has a value of 1 when U=RRSiO andy+l when U=RSiO x is an integer having a value of from 10 to about 10 yis an integer having a value of from 1 to about 10 the sum of x, y, andq being such that the silicone compound MD U M, has a molecular weightof from about 10 to about 10 and the ratio of epoxy-containing units tounits containing no epoxy groups is within the range of from about 0.001to 0.5, preferably from about 0.01 to about 0.25. Illustrative of themonovalent hydrocarbon radicals represented by R in the units definedabove for U are alkyl groups containing from 1 to 10 carbon atoms, morepreferably 1 to 6 carbon atoms, such as methyl, ethyl, propyl, butyl,isobutyl, amyl, hexyl, octyl, and decyl; alkenyl groups such as vinyl,allyl, butadienyl, and l-pentenyl; aryl radicals including fused ringstructures such as phenyl, p-phenylphenyl, naphthyl, anthryl and thelike; alkaryl radicals such as tolyl, xylyl, p-vinylphenyl, andB-methylnaphthyl; aralkyl radicals such as stearyl, phenyl-methyl andphenyl-cyclohexyl; and cycloalkyl radicals such as cyclopentyl,cyclohexyl and cyclobutyl. Preferably, R is an alkyl radical, and moreespecially a methyl radical. The monovalent organic radicals representedby R which contain epoxy groups are, exclusive of the oxirane oxygennecessarily present, preferably hydrocarbon radicals free of acetylenicunsaturation or containing in addition to carbon and hydrogen only etheror carbonyl oxygen. Such R radicals include 3,4 epoxycyclohexyl; 6methyl 3,4-epoxycyclohexyl; 3- oxatricyclo [3.2.l.0 ]octane 6 propyl;7-butyl-3-oxatricyclo [3.2.1.0 ]octane-6-methyl; 3,4-epoxycyclohexyl-1-ethyl; 9,10-epoxystearyl; 8-glycidoxypropyl; p(2,3-epoxybutyl) phenyl;and 3-(2,3-epoxy-butyl) cyclohexyl. The vicinal epoxy group can be, butneed not be, a terminal group of the R radical. Moreover, the R radicalcan be simply a H O JL CH.

radical directly joined to silicone.

Additional illustrations of suitable epoxysilicones are set forth in theJournal of the American Chemical Society, vol. 81, pages 2632-2635 (June5, 1959). A still further silicone compound which may [be employed intreating the paper cover sheet is an addition product of a hydrosiliconecompound with a fatty acid ester containing, for example, at least oneunsaturated carbon-to-carbon bond, wherein the addition product containsfrom about 0.2-85% silicone. Preferred fatty acid esters are drying oiland semi-drying oil. The preferred addition products have the followinggeneral unit formula:

where R is a monovalent hydrocarbon group, x has a value of from to 60,and y has a value of from 1 to 60. The following examples furtherillustrate our invention:

Example 1 In treating the paper cover sheet in accordance with thisinvention, a methyl hydrogen polysiloxane having the general structureshown in Formula 1 was used. This polysiloxane is a fluid having aspecific gravity at 25 C./25 C. of about 1.01 to 1.02, a viscosity offrom to 40 centistokes and has the appearance of a clear liquid. Anemulsion of this polysiloxane was prepared employing 40% by weight ofthe polysiloxane, 7 /2% of a conventional emulsifier (a polyoxyethylenederivative of polyhydric alcohols), and about 52.5% by weight of water.The emulsion was prepared using conventional emulsion formingtechniques. An aqueous emulsion of dibutyl tin dilaurate (37.5% byweight) was employed as the curing catalyst. Applicator troughs wereplaced at the bottom nip of the wet calender stack to effect thetreating of the bottom liner ply. The methyl hydrogen siloxane wasapplied at the applicator trough at the dry calender stack and thecuring catalyst was applied by means of the applicator trough located atthe wet calender stack. The hydrophobic silicone emulsion was diluted toapply 1.5 pounds of solids per ton of paper. Similarly, the curingcatalyst emulsion was diluted to permit .7 pound of catalyst per ton ofpaper to be applied. The treated paper had Cobb values after being curedfor 24 hours at 90105 F. of about 0.4-0.6 gram. The treated paper coverwas employed in manufacturing /3 inch thick gypsum wallboard. Aconventional gypsum slurry was used in preparing the core with theexception that the core contained only about 0.4% by weight of starch,which is a clear reduction from conventional requirements of about 0.8%by weight. In addition, the rosinalum size was omitted from the bond plyand the adjacent filler ply thereto, thereby resulting in a secondsubstantial savings.

Comparative tests of gypsum wallboards were run where the wallboardswere subject to humidification for 18 hours at 90 F. and 90% relativehumidity. Wallboard using paper cover sheet not treated in accordanceExample 2 In this example of treating the paper cover sheet inaccordance with this invention, there was used an epoxy silicone polymerhaving the average formula as:

This epoxy silicone is a fluid having a specific gravity at C./25 C. ofbetween about 0.99 to 1.0. An emulsion of this epoxy silicone wasprepared by employing 40% by weight of the silicone. The epoxy siliconewas applied to the bottom liner ply of the paper cover sheet at thebottom nip of the wet calender stack. No catalyst was employed in thisapplication. The epoxy silicone emulsion was diluted to apply 0.5 poundof solids per ton of paper. The treated paper had Cobb values afterbeing cured for 10 days at room temperature of about 0.4 to 0.6

gram. The paper was used in the manufacture of /2 inch gypsum wallboard,and the resulting board evidence 100% paper to core bond. Here again,there was about a 50% reduction in starch usage, and no rosin-alumsizing was employed in the bond ply and the filler ply immediatelyadjacent the bond ply.

Example 3 A paper cover sheet was made in accordance with this inventionusing an addition product of a hydrosilicone compound with a fatty acidester having the general structure shown in Formula 5. The additionproduct was applied to the bond ply of the paper cover sheet by rollerapplication in an amount of 0.8 pound of solids per ton of paper and nocatalyst was employed. The paper was cured at F. for 5 days, andrendered a Cobb value of 0.7 gram. The treated paper was employed inmaking /2 inch wallboard by a batch type method. Here again, the boardevidenced paper to core bond at a substantial reduction in the quantityof starch used in the gypsum core, and no rosin-alum sizing was employedin the bond ply and the three filler plies adjacent the bond ply.

Although the foregoing invention has been described with reference toillustrative embodiments and other details of the invention, it isapparent that variations and modifications can be carried out withoutdeparting from the scope of this invention. Accordingly, the inventionis defined by the scope of the appended claims.

What is claimed is:

1. Paper-covered gypsum board which comprises a gypsum core and a papercover sheet covering at least one side of said core, said paper coversheet having a cured hydrophobic organo-silicone in an amount sufiicientto attain in said sheet, when said board is manufactured, a Cobb valueof about 0.4 to 1.0 gram measured on the surface of said sheet adjacentsaid core.

2. A paper-covered gypsum board according to claim 1 wherein said Cobbvalue is from about 0.4 to 0.7 gram.

3. A paper-covered gypsum board in accordance with claim 1 wherein saidsheet contains 0.1 to 4 pounds of said hydrophobic silicone per ton ofsaid sheet.

4. A paper-covered gypsum board in accordance with claim 1 wherein saidsheet contains 0.2 to 2 pounds of said hydrophobic silicone per ton ofsaid sheet.

5. A paper-covered gypsum board according to claim 1 wherein said curedhydrophobic silicone is selected from the group consisting oforganohydrogen siloxanes, epoxy silicones and the addition products ofhydrosili cone with a fatty acid ester.

6. A paper-covered gyspurn board in accordance with claim 1 wherein saidpaper cover sheet is a multi-ply paper cover sheet and the space fromthe surface of said sheet adjacent said gypsum core to a locationdisplaced inwardly of said sheet from said surface contains said curedhydrophobic silicone.

7. A paper-covered gypsum board in accordance with claim 6 wherein thebond ply of said multi-ply paper cover sheet contains substantially norosin and alum sizing compound.

8. A method of making paper-covered gypsum board which comprises forminga core of cementitious gypsum slurry, laminating said core with a papersheet containing a cured hydrophobic silicone in the space from thesurface of said sheet placed adjacent said gypsum core to a locationdisplaced inwardly of said sheet from said surface in an amountsufiicient to attain in said paper cover sheet a Cobb value of about 0.4to 1.0 gram as measured on the surface of said sheet adjacent said coreand drying said gypsum board.

9. A method according to claim 8 wherein said hydrophobic silicone isselected from the group consisting of organohydrogensiloxanes, epoxysilicones, and the addition products of a hydrosilicone with a fattyester.

10. A method according to claim 9 wherein said cured hydrophobicsilicone is an organohydrogensiloxane.

11. A method according to claim 9 wherein said cured hydrophobicsilicone is an epoxy silicone.

12. A method of making a paper-covered gypsum board which comprisesapplying a hydrophobic silicone to a paper cover sheet for gypsum boardat the zone adjacent the gypsum, said hydrophobic silicone selected fromthe group consisting of organohydrogensiloxane, epoxy silicone and theaddition product of a hydrosilicone with a fatty acid ester, curing saidhydrophobic silicone, forming a core of cementitious gypsum slurry,laminating said core with a paper cover, and drying said gypsum board,the cured hydrophobic silicone being present in an amount sufiicient toattain in said paper cover sheet a Cobb value of about 0.4 to 1.0 gramas measured on the surface of said sheet adjacent said core.

13. A method of making a paper-covered gypsum board which comprisesforming a paper cover sheet, applying to at least one side of said sheeta hydrophobic silicone, curing said hydrophobic silicone, forming a coreof starch-containing cementitious gypsum slurry, 1aminating said coreand said sheet with a side of said sheet having said hydrophobicsilicone applied thereto in contact with said core to produce a gypsumboard, and drying said gypsum board, the amount of said curedhydrophobic silicone being sufficient to attain in said sheet a Cobbvalue of about 0.4 to 1.0 gram as measured on the surface of said sheetadjacent said core.

14. A method of making a paper-covered gypsum board which comprisesforming a multi-ply paper cover sheet and calendering said resultingsheet, applying a hydrophobic silicone to at least one surface of saidsheet during said calendering, said hydrophobic silicone selected fromthe group consisting of organohydrogensiloxane, epoxy silicone and theaddition product of a hydrosilicone 14 with a fatty acid ester, curingsaid hydrophobic silicone applied to said sheet, forming a core ofstarch-containing cementitious gypsum slurry, laminating said core andsaid sheet with a side of said sheet having said hydrophobic siliconeapplied thereto in contact with said core to produce a gypsum board, anddrying said gypsum board, the amount of said cured hydrophobic siliconebeing sufiicient to attain in said paper a Cobb value of about 0.4 to1.0 gram as measured on. the surface of said sheet adjacent to saidcore.

15. A method according to claim 14 wherein the amount of said curehydrophobic silicone is from 0.1 to 4 pounds per ton of paper.

16. A method according to claim 14 wherein said hydrophobic siliconeapplied to said sheet is cured with a catalyst.

17. A method according to claim 14 wherein said bydrophobic silicone isa methyl hydrogen polysiloxane.

18. A method according to claim 14 wherein said bydrophobic silicone isepoxy silicone.

References Cited UNITED STATES PATENTS 2,342,462 2/1944 Farmer et al.15644 X 2,352,553 6/1944 Lefebure 1564l 2,560,521 7/1951 Camp 156412,774,690 12/1956 Cockett et al 260--448.2 2,806,811 9/1957 Von Hazmburg156-39 X 3,227,579 1/1966 Bluestein 117161 2,785,067 3/1957 Osberg162158 3,307,987 3/1967 Bieri 15641 EARL M. BERGERT, Primary Examiner.

T. R. SAVOIE, Assistant Examiner.

